Although an end mill is used, for example, in a grooving process and a shouldering process of a workpiece, it is necessary to smoothly discharge chips generated by cutting off. For this purpose, chip discharge performance is improved by forming a chip discharge flute between a plurality of outer peripheral cutting edges. For example, as illustrated in Japanese Unexamined Patent Publication No. 2015-080844 (Patent Document 1), a gash for forming a bottom cutting edge is disposed at a front end side of the chip discharge flute in the end mill.
However, a chip discharge state of the grooving process differs from that of the shouldering process. Particularly, in the grooving process in which a large amount of chips are generated, chip clogging may occur. When the chip discharge flute is made deeper, a core thickness of an end mill body decreases, and rigidity of the end mill body is lowered. Therefore, in the shouldering process subjected to a large resistance exerted in a direction orthogonal to a rotation axis of the end mill body, the end mill body may significantly bend, and machining accuracy of the end mill may be lowered.